`benchmark.yml` triggers repeatedly on merging benchmark results to master

[maxonfjvipon]

The benchmark.yml is triggered on push to master branch and opens a new pull request with new benchmark statistics. However, when these new benchmark results are merged to master, benchmark.yml will be triggered again and make new pull request. And it's an infinite process until we stop it using paths-ignore option. Use this as example.

[maxonfjvipon]

@yegor256 FYI

[0crat]

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